This invention relates to a concept that monitors system conditions in a refrigerant cycle, and reduces the compressor load should those conditions approach an extreme condition, in order to prevent system nuisance shutdowns and complete loss of cooling load by end users.
Refrigerant cycles are utilized for HVAC systems, refrigeration units, and various other applications. In conventional refrigerant cycles, a compressor compresses a refrigerant and delivers that refrigerant to a condenser. From the condenser, the refrigerant travels to an expansion device, and from the expansion device, to an evaporator. From the evaporator, the refrigerant is returned to the compressor.
One recent development in the refrigerant cycle art is the inclusion of an economizer cycle. In an economizer cycle, a portion of the refrigerant downstream of the condenser is tapped off and passed through an economizer expansion device, and then into an economizer heat exchanger. The main refrigerant flow from the condenser also passes through the same economizer heat exchanger, preferably in a counter-flow arrangement. In the economizer heat exchanger, the tapped flow cools the main refrigerant flow. In this manner, a greater cooling capacity is provided by the main refrigerant flow. Downstream of the economizer heat exchanger, the tapped refrigerant is returned to the economizer port of the compressor.
Motors for compressors in a refrigerant cycle are often provided with a shut-off protection device. These shut-off protection devices can shut down the motor of the compressor should an excessive current be experienced. Moreover, if motor temperature becomes too high, the protection device may also open, shutting down the motor.
In many extreme load situations, such as when the ambient temperature is high, and line voltage is low, the condition may cause the protection device switch to actuate, and stop the motor. Of course, the conditions when the ambient temperature is high would not be a good time for the refrigerant cycle to be shut down, since at such conditions cooling load is needed and desired the most by end users. As such, one time when the protection switch is quite likely to stop operation of the motor, is also a time when it would be the least desirable.
One challenge for a refrigerant cycle designer, and in particular for the compressor designer, is to keep the overall size of the compressor housing small. At the same time, a motor for the compressor must be sufficiently large to be able to drive the compressor at the extreme load conditions mentioned above.